A medical pressure sensitive adhesive tape has a structure that a pressure sensitive adhesive layer is formed on at least one side of a base material. Since the medical pressure sensitive adhesive tape is intended to be applied to human skin, and often applied over a long period of time, it is designed after due consideration so as not to cause rash.
Specifically, as a base material of the medical pressure sensitive adhesive tape, is generally used a fabric, nonwoven fabric, plastic film, Japanese paper or the like having good flexibility and gas permeability. In order to prevent sweat generated by sweating from remaining in a site applied, a base material made of a material having excellent moisture permeability is also used. Further, a base material having good stretchability so as to permit conforming to the movement of human skin has been developed.
As a pressure sensitive adhesive for the medical pressure sensitive adhesive tape, a pressure sensitive adhesive such as the rubber, acrylic or silicone type, which neither exerts a sensitizing effect on skin nor causes marked skin irritation, is used. In order to prevent the occurrence of contact dermatitis by the adhesive tape, components constituting the pressure sensitive adhesive are generally selected from among raw materials that have borne good results and considered so as not to cause allergic dermatitis. In addition, the use of chemical substances strongly irritating the skin is avoided to the utmost to prevent the occurrence of dermatitis caused by a specific chemical substance.
The adhesive strength of the medical pressure sensitive adhesive tape is required to be sufficiently high to an extent that absorbent cotton, gauze, bandage, catheter, tube, poultice or the like can be fixed. On the other hand, the adhesive strength of the medical pressure sensitive adhesive tape is controlled so as to lower to an extend that the horny layer on skin surface is not markedly separated upon the peeling of the pressure sensitive adhesive tape, thereby avoiding causing rash.
As described above, the medical pressure sensitive adhesive tape is designed in vie of the kind of the base material, components of the pressure sensitive adhesive, level of adhesive strength, etc. in such a manner that it has moderate adhesive strength and moreover no rash is caused on the skin. However, the conventional medical pressure sensitive adhesive tapes have actually involved a problem that contact dermatitis such as rash is often caused on skin. It has also been difficult to balance the lightening of skin irritation with adhesive properties.
From the viewpoint of the skin irritation, the contact dermatitis by a medical pressure adhesive tape is generally such that erythema or papula attended with itch is caused on a site applied, unlike grave dermatitis spreading over a wide range, such as urusi (Japanese lacquer) poisoning. However, in an actual medical field, a medical pressure sensitive adhesive tape must be often applied over a long period of time or repeatedly many times on a specific site. In such a case, erythema or papula is worsened into blister, so that the epidermal part of the skin is in a damaged state. Namely, the patient comes to undergo a side effect attendant on treatment. In order to prevent such a side effect, it is necessary not to irritate the skin as much as possible. However, the conventional medical pressure sensitive tapes have been unable to cope with this requirement.
From the viewpoint of the adhesive properties, a necessary level for adhesive strength to human skin is determined by conducting practical experiments such as fixing of gauze. Accordingly, medical pressure sensitive adhesive tapes having adhesive strength to an extent that gauze or the like can be fixed to most persons without any problem under various service conditions have heretofore been developed and provided. However, the adhesive strength of a medical pressure sensitive adhesive tape to human skin may be often changed with time. For example, when the moisture permeability of the medical pressure sensitive adhesive tape is too low, sweat remains between the skin surface and the pressure sensitive adhesive layer when sweating occurs during sticking of the adhesive tape. As a result, the adhesive strength of the medical pressure sensitive adhesive tape is lowered with time, resulting in a failure to fix and hold gauze or the like.
In order to solve the above-described problem, it is only necessary to enhance the adhesive strength of the pressure sensitive adhesive so as to retain such adhesive strength that gauze or the like can be fixed even when sweating occurs. This method has been a general solving means from before. However, when the adhesive strength of the medical pressure sensitive adhesive tape is enhanced, such a medical pressure sensitive adhesive tape comes to have too high adhesive strength to the skin when no sweating occurs. As a result, a degree that the horny layer on the skin surface is simultaneously separated upon the peeling of the medical pressure sensitive adhesive tape is increased, so that dermatitis is liable to occur. In addition, when the adhesive strength of the pressure sensitive adhesive is enhanced with time, the pressure sensitive adhesive may remain on the skin surface upon the peeling of the medical pressure sensitive adhesive tape in some cases.
The above problem can be lightened to some extent by using a base material having excellent moisture permeability. However, the moisture permeability of a medical pressure sensitive adhesive tape not only depends on the moisture permeability of a base material, but also is greatly affected by the kind or the like of a pressure sensitive adhesive. When the moisture permeability of the pressure sensitive adhesive is low, the moisture permeability of the resulting medical pressure sensitive adhesive tape may become insufficient in some cases even when a base material having good moisture permeability is used. On the other hand, even when a pressure sensitive adhesive having good moisture permeability is used, or a method of making the structure of a pressure sensitive adhesive layer excellent in moisture permeability is adopted, it is difficult to balance the lightening of skin irritation with adhesive properties when the adhesive strength to human skin is insufficient, or the adhesive strength to human skin is decreased or increased with time, or cannot sufficiently conform to the extension and contraction of skin at a site applied.
The adhesive strength of a medical pressure sensitive adhesive tape can be objectively evaluated by, for example, measuring its adhesive strength to bakelite plate or stainless steel plate, whereby the composition and the like of a pressure sensitive adhesive can be adjusted so as to have moderate adhesive strength. However, this measured value of the adhesive strength does not stand in a simple proportional relationship to the adhesive strength when the medical pressure sensitive adhesive tape is actually applied to human skin. On the other hand, the adhesive strength of a medical pressure sensitive adhesive tape is measured by applying the adhesive tape to human skin, the adhesive strength varies with time, so that the adhesive strength often decreases or increases. The correlation between the physical properties of a pressure sensitive adhesive, such as adhesive strength, and skin irritation is also not said to have been sufficiently elucidated. Even from the viewpoint of controlling the physical properties of the pressure sensitive adhesive, such as adhesive strength, it has been a difficult problem to provide a medical pressure sensitive adhesive tape excellent in practical performance.
As described above, the mechanism of irritation given to human skin when a medical pressure sensitive adhesive tape is applied to the skin is not said to have been fully elucidated. In a medical field, it is strongly required to lighten the pain of a patient. Although it is important from the viewpoint of providing a medical pressure sensitive adhesive tape excellent in practical performance that the material and form of a base material, the composition and adhesive properties of a pressure sensitive adhesive, etc. are suitably selected and combined with each other, there is a demand for planning to provide a medical pressure sensitive adhesive tape balanced between the lightening of skin irritation and adhesive properties at a high level by approaching the mechanism of skin irritation from a new point of view.